It is well known that in many engines the fuel is the lubricant for the fuel system components, such as fuel pumps and injectors. Many studies of fuels with poor lubricity have been conducted in an effort to understand fuel compositions which have poor lubricity and to correlate lab test methods with actual field use. The problem is general to diesel fuels, kerosene and gasolines, however, most of the studies have concentrated on the first two hydrocarbons.
Previous work has shown that saturated, monomeric and dimeric, fatty acids of from 12 to 54 carbon atoms used individually give excellent performance as fuel lubricity aids in diesel fuels. While these materials show excellent lubricity properties, they are often difficult to formulate into products due to their poor solubility in hydrocarbons and fatty acid mixtures. Commercial product TOLAD.RTM. 9103 Fuel Lubricity Aid sold by Baker Petrolite Corporation only contains approximately 3.8 weight %, stearic acid (a saturated monomeric fatty acid) in a specific and complex mixture of unsaturated monomeric and unsaturated oligomeric fatty acids and heavy aromatic solvent. It has performance characteristics better than products which do not contain the high levels of these saturated acids. However, levels of stearic acid higher than 3.8% tend to separate from the product on standing which limits their usefulness as additives. Simply increasing the stearic acid proportion in TOLAD 9103 Fuel Lubricity Aid above about 3.8% results in an unstable product.